Pneumatic percussive tool



ug. 3, 1937. Q BRUN PNEUMATIC PERcUsslvE TOOL s sheets-snaai Filed Jan. 25, 1935 Aug. 3, 1937. G. BRUN PNEUMATIC PERCUSSIVE TOOL Filed Jan. 23. 1955 s sheets-sheet 2 ug. 3, 1937. Q BRUN PNEUMATIC PERcUssIvE TooL Filed Jan. 25, 1935 3 Sheets-Sheet 3 Patented Aug. 3, 1937 A usaran sTATss PATENT oFF-ICE PNEUMATIC' PERCUSSIVE TOOL Georges Brun, Saint-Etienne, France, assigner to Socit dEtudes et dExploitation du Genrateur Piston Libre, acorporation of France Application January 23, 1935, Serial No. 3,138

In France January 23, 1934 8 Claims. (Cl. 121-30) The present invention relates to a pneumatic referring t the diagram' illustrated ih Figure 1 tool which can be used for the most varied purof the accompanying drawings. poses piercing, cutting, riveting, etc.) and which The main piston comprises a large diameter is very powerful and highlyfeiicient in operation. head' dl' movable' irl a Cylinder l? provided With The power of usual pneumatic tools is limited admission oriiices bi1 and exhaust orifices b2 and a 5 because the speeds of the piston at the moment plunger DiSlOn 0f Small diameter a2 mOi/able in a of impulse must not exceed three to four meters Cylinder C' CO-aXial With the Cylinder b- The' DiS- per second and on the other hand the eciency t0n Carrying i001 d Slides in' ChefrOIit end 0f this is low. same cylinder c. The cylinder c passes through a lO Experience has shown in fact that the best Chamber e frOm Which leadsV a dllCi Whieh 'lo steels known only withstand repeated impacts communicates with a bore g in Which Slides a if the speed of impact does not exceed the above block h- The space comprised between the pisstated limit, ton a2, the tool holder d and the block h. is filled Further, the efficiency is low chiey because With Oil; the lfae` 0f thev blOCk OPDOSiie-thai l5 a great part of the kinetic energy of the piston which is in contaotfwith the oil ist subjected t0V 15 is destroyed through the impact by the elasticy the pressure of the Compressed air. hysteresis and unnecessary vibrations and in ad- The Operation' iS aS fOllOWS When the PiSlOh dition on account of the fact that the distribual. a2. is et the left-hand endV of its stroke andtion of compressed air motors is of an elementary the admiSSiOh Orifice' lil iS 019er!y lihe PSOII a nature, accelerates'in aforward direction. As long as 20 In practice with a bore of 40V to 5o m/m. for the plunger a2 has not passed beyond the' chamthe air cylinder (toois working in an directions) ber e the oil Willv be displaced in the duet f and useful powers are obtained of 20 to 30 kg. at the IhOVe the blOCk h against` the` pressure 0f the point of the tool. with bores of 60 to 75 m/m. Compressed' air. At the end of e Certain travel piercing tools working in a downward direction) the piston a2 travellingv et full speed passes be- 25 the useful power reaches 1;@` 50 kg The conyond the chamber e; The oil interposedY between sumption of compressed air corresponds to a a2 and the tool holder ai is violently compressed pneumatic power which is 5 to 10 times greater. While the SDeed'Of the DSOD dl, aSlaCkeDS and In the tool according to the invention, a colthe t001y holder d TeCeiVeS the impulse Which 30 umn of liquid, for example oil, is interposed Causes it to advance against the workpiece which. 30

between the piston moved by the compressed iS ODDOSed t0 it. air and the e001 at the moment of impulse, the In the meantime the admission has closed and. volume of this liquid being calculated in such the exhaust orifices have Opened- When the a Way that the pressures Wm be limited by the pistonY a/ hascometo rest itis driven backwards 35. oompressibility of the oil to admissible values. (vthe-Betumngmeans are n0t--sh0wn inthe draw 35 The speed of the compressed air piston at the mi? inguite ramtlocslns Ilvl of gneerclno eleOrnymb/nragdsgog the block h for .the distribution of the compressed is th u .t.n 1 th s f d. t t air. For this purpose the orifice b=1 leads 1nto e I m 1 g Va ue m e Ca ,e o 1re? lfnpac' the wall of the cylinder g. They are covered 40 Thf@ ilmltmg power for a' gwen recon 1S thus by the block h when thek forward stroke of the multlphed by Vej Y piston has reached a suitable value and are Further the 011 interposed bei/Ween the all uncovered in the opposite direction through the piston and the tool holder forms a perfect spring backward str-Oke when the piston. is sumcently .i5 having no hysteresis and the period of vibrationy close to the end of the cylinder b. 4o of the system is much higher than the periodici The construction of a tool of this type gives vibration proper of the air piston and of the rise to a certain number of diicultieswhich tool holding piston. The energy dissipated by necessitate the use of special devices that will unnecessary vibrations is greatly reduced and be enumerated hereinafter before proceeding tol the efciency is considerably increased. the detailed description. 50

in this way very handy tools can be constructed 1. It is necessary in spite of leakages to mainhaving a useful power reaching several huntain a certain quantity of oil between the pistons dred kg. a2, dand h; for this purpose; a reservoir of oil The principle of the tool according to the under` pressure orVv feeder must be provided and' o5 invention will be more clearly' understood by also means of communication between thefeeder r and the chamber defined above,` such that at the end of the backward stroke of the main piston the block h will abut against the front end of the cylinder y without vacuum being produced.

2. The oil delivered by the piston a2 before the impact is driven forward by the latter its inertia damps the forward stroke and a great part of the corresponding kinetic energy is lost. It is therefore of interest to reduce to a minimum the inertia l of the column of oil comprised between the chamber f and the block h. In the machine described in detail hereinafter a differential' piston has been arranged in the immediate neighbourhood of the chamber f which differential piston reduces the volume of oil delivered to the sliding block h to a fraction of the volume of the oil delivered by the piston a2.

3. The sliding block h as described above has a movement which synchronizes with that of the piston a1. Under these conditions the admission opens upon the backward stroke and closes upon the forward stroke for the same position of the piston. Theanticipated admission equals the true admission, it being understood that the term anticipated admission implies the stroke of the piston in front of the rear dead point from the position where the admission is open up to said point and the term true admission implies the stroke of the piston after it has reached the rear dead point from the latter to the position where theadmission closes. It is of interest to reduce the anticipated admission with respect to the true admission and therefore to displace the movement of the slidingblock so as to make it lag behind the movement of the main piston.

4. It is necessary to provide an admission of compressed air against the forward face of the piston a1 at the commencement of the backward stroke and alsoto provide distribution means. Y

In the lmachine described in detail hereinafter this vdistribution is automatic.

5. The tool holder is provided with an abutting collar which limits its displacement forwardly with respect to the body of the tool. It is necessary that the space between thiscollar and the front end of the tool 'is lled with oil so that in case of an abnormal displacement forwardly of the tool holder, as when the resistance to the forward movement of the tool holder is negligible,

the impact of the collar against the end of the tool body is damped during the expulsion of the oil.

' 6; In the hydraulic transmission tool, as compared to direct impact tools, the position of the main piston at the momentv of impulse is unvarying; it is the position for which 'the plunger a2 is flush with the forward edge of the chamber e. In direct'impact tools the forward displacement of the shank of the tool is utilized in the idle operation (without opposed resistance) in order to damp the kinetic energy of the air piston by the compressionof the air between the front face of this piston and the front end of the air cylinder,

@5 and these tools operate without impact on no load. In thehydraulic transmission tool, if the admission wereY maintained constantly on no load violent compressions would be produced between the piston CL2 and the tool holder locked against the forward abutment. In order to avoid this, an automatic stopping device must be provided which cuts off the admission of compressed air when the tool holding piston approaches its forward abutment. (Such devices are not novel and are g5 provided upon certain direct impact piercing hammers but they are indispensable in a hydraulic transmission tool.)

7 Finally, in the diagram shown in Figure l the same diameter has been given to the piston a2 and to the tool holding piston d. It may be of advantage to give the piston d a larger diameter than the piston a2 in order to increase the instantaneous forces and the weight of the tool without rendering the main piston heavier. This latter arrangement is that of the machine described in detail hereinafter. It does not increase substantiallyl the recoil of the machine when the tool is free, or advances rapidly, provided that the weight of the tool is properly adjusted, butV it enormously increases the recoil when the tool is locked or advances slowly, as a consequence of reactions upon the annular end of the bo-re of the tool holding piston while the piston a2 rebounds upon the column of oil. In order to prevent the tool from becoming blocked under these conditions, when the resistance is too high according to the invention, a so-called recoil piston is keyed upon the tool holding piston. This recoil piston is movable in a cylinder xed to the body of the machine and is subjected to the pressure of compressed air on its front face and to atmospheric pressure on its back face. In this way the recoil is balanced if the tool is jammed; if it is not jammed it is separated at the moment of impulse from the material acted upon so that it acts as a free tool and the recoil remains weak.

There are obviously many ways of carrying out these various conditions. By way of example one particular embodiment will be described hereinafter but it is understood that the invention may include other modifications of detail.

Figure l is a diagrammatic view of a machine for carrying out the principle of the invention.

Figures 2 and 2A illustrate a general section of the machine, the section being shown in such a way as to make all the essential details appear.

Figure 3 is an enlarged detail View of the plunger Il and the re-feeding valve.

Figure 4 is an enlarged section of the double valve interposed between the slide valve and the differential member.

In these gures, I is the compressed air cylinder, with the admission orifices l1 for accelerating the piston, the exhaust orifices l2 and the admission orices I3 for the return. In this cylinder reciprocates the air piston 21, which is rigid with the plunger 22 slidably mounted in the sleeve 3 which is co-axial with the cylinder I.

This sleeve communicates with the large chaml ber filled with oil comprised between the parts 'l and 4 (engaged in the body of the machine). The member 4 is provided with a bore 4 therein coaxial with the plunger 22 and of the same diameter. The bore 42 is a counter bore also coaxial with the plunger 22.

When, at the end of the forward stroke the plunger 22 engages in the bore 41, it violently compresses the oil interposed between the piston 22 and the piston 5 and imparts an impulse to this piston. Apart from this stage which is of short duration, the piston 22 is not engaged in the bore 41 and in delivering or drawing in oil, it produces the reciprocation of the annular differential piston 6 which closes the oil chamber at the back. The section 61 of this piston towards the front'is much greater than the section of the plunger 22 in order to reduce the inertia and the absolute displacements of the differential piston 6. Towards the back, the differential piston 6 has an annular face 63 in open communication through orices I1 with the feeder 8 which will be described hereinafter and an annular face 62, the section of which is only a small fraction of the face 61 (1/3 to 1/5). By means of this face 62 sliding in the bore 'l2 the differential piston delivers a volume of oil proportional to the displacement of the main piston through the large duct 'i4 to the slide Valve S (through the valves l2, i3, the function of which will be described hereinafter). The inertia of the column of oil interposed between the slide valve 9 and the main piston is thus considerably reduced.

The feeder will now be described: the latter is a reserve of oil maintained at the pressure p of the compressed air in Il) in front of the slide Valve 9. It is lodged in a chamber 82 of the tool body, communicating throughducts l5 with the pressure p. The reserve of oil is separated from the air by the diaphragm 81 made of flexible rubber which is not attacked by oil. The pressure of the oil is thus maintained equal to pi; as the reserve of oil becomes exhausted the diaphragm is deformed accordingly.

The feeder at the same time as it absorbs and restores periodically a greater part of the oil delivered by the piston 22 maintains a full supply of oil between the differential piston, plunger 22 and tool holder and also between the differential piston 6 and the slide valve. In the event of a lackA of oil between the differential piston, plunger 22 and the tool holder, the differential piston abuts forwardly against the member 4. In this position it uncovers at the rear the grooves 'l5 which put the above described space and the feeder into communication witheach other so that a Vacuum cannot be produced.

On the other hand, in the event of an excess of oil the differential piston abuts at the rear against the end of the bore 12 and at the front uncovers thegrooves 'i6 through which the excess of oill delivered bythe plunger 22 goes to the feeder.

A description will be given hereinafter of the manner in which the feeder ensures a full quantity of oil between the differential member 62 and the slide valve 9. The feeder 8 must be recharged periodically. It is easy to dimension it so that the provision of oil will be amply sufcient for eight hours of uninterrupted working.

The slide valve and the arrangements adopted for regulating the admission will now bei described. It will be assumed that when the piston 2 is at the end of its backward travel the slide Valve 9 abuts at the front against the rear face of the' seat of the member l2 without Vacuum being produced (hereinafter a description will be given of the means of communication between the feeder and the chamber interposed between the slide valve and the differential member which permits this result to be obtained very simply). In this position the slide Valve uncovers the outlet of the orifices il in the bore I0; the admis- 'sion beingwide open.

If the walls of the chamber comprised between the end of the bore l2 and the end of the bore in the slide valve were indeformable, the strokeV the backward stroke.' Under these conditions the slide valve which has come into abutment at the commencement of the forward stroke of the piston 2 will remain stationary while the increase is produced in the chamber and the true admission stroke will be increased relative to the anticipatedadmission stroke by thel displacement of the piston 22 corresponding to the additional volume delivered by the differential member 62.

This increase in capacity at the commencement of the forward stroke will be obtained in the following manner: A double valve i2, i3 is interposed between the differential member 62 and the slide valve 9. The valve l2 which is pushed backwards bythe spring H21, produces a given loss of charge, upon the passage of oil from the slide valveto the differential, which loss of charge is moreover small. As the slide valve 9 is subjected on its back face to the pressure p of the compressed air, the oil pressure on the differential member S2 during the backward stroke of the main piston (the oil then goes from the slide valve to differential member) is. pthe said loss of charge (approximately in View of loss of charge and inertia effects). During the forward stroke of the main iston the oil passes from the differential member 62 to the slide valve. The valve i2 is then pressed upon its seat; the oil passes through the orifices l22 and lifts the Valve I3 which is movable within the valve l2 and is strongly loaded by the spring H31. This Valve I3 produces a greater loss of charge and the oil pressure at the differential member is p-ithe loss of charge.

In order to produce a required-increase of capacity it is sufficient to interpose between the feeder at the pressure p and the chamber i3 into which the bore l2 leads, a piston movable between two stops. Y

This piston will move automatically against the pressure of the feeder at the commencement of the forward stroke and against the'pressure of the oil in 'I3 at the commencement of the backward stroke.

This piston is illustrated at il, Fig. 3; it

slides in the bore H2 formed in the ring which sepa-rates the chamber 'i3 from. the feeder and its stroke is limited by two stops. It is pushed forward against the pressure in the chamber 73 by a spring ill, Fig. 2 which balances a pressure p1 such that p+p1 will be the mean of the pressures' p modied, as described by the action of the valves i2 and I3.

A description will now be given of the means employed for keeping the chamber between the slide valve 'and the differential member full of oil by ensuring that at the end of the backward stroke of the main piston the slide valve will abut at the front against the seat of the valve i2.

The chamber 'i3 communicates with the end of the bore 'l (that is to say with the feeder since the end of this bore communicates with the feeder through the orifices 11) through an orifice closed by an automatic valve M, which lifts against the reaction of the spring M2 in order to allow oil to pass from the feeder to the chamber 13.

The wall of this valve is provided with orifices |41. As the mean pressure in the chamber i3 is greater than p during a double stroke, that is to say, a forward and backward stroke of the slide valve a small quantity of loil escapes through the orifices |41 to the feeder, thereby ensuring that the slide valve il will abut against the seat of the valve |2 a little before the end'of the backward stroke.

A vacuum can, moreover, not be produced because the valve |4 then lifts and the feeder restores the oil which has escaped through the preceding double stroke.

A description will now be given of the means employed for ensuring the return of the main piston. An account has been given above of the manner in which the admission by the forward stroke was regulated to a fixed value.

A certain time after the slide valve has closed the admission, the piston 21 in moving forward closes the exhaust orifices |2 at the front and commences to compress theair between its front face and the front end of the cylinder A short time later it uncovers the orifices |2 at the rear and the pressure falls rapidly behind the piston 21. Finally, a little time afterwards, the plunger 22 engages in the bore 41 and is rapidly damped by the compression of the oil between 22 and 5. The piston 2 then stops. The expansion of the air between the front face of 21 and the end of the cylinder and also if desired the rebound of the piston 22' on the compressed oil (the latter effect moreover being variable according to the resistance opposed to the tool) tend to return the piston 2 backward but these two 4effects are insufficient to ensure a considerable stroke backwards.

The energy stored by the compression between the front end of the cylinder E and the piston is in fact constant in absolute value while the energy supplied to the piston through the forward stroke depends upon the pressure p.

If this pressure falls the kinetic energy of the piston 2 may be absorbed by the compression of the air at the front end and the machine would cease to produce a useful effect.

It is, therefore, practically necessary to admit compressed air at the commencement of the backward stroke between the front end of the cylinder I and the piston 2. This admission is ensured as follows on the machine described.

The admission orices |3 at the front of the cylinder lead into a chamber |84 separate from the chamber |52 in which the pressure p exists by means of a valve I8. The valve is formed by a flat wall which rests upon the seat |65 having an internal section S1 and a cylindrical guide- .way |82 sliding in a bore of section S2 a little less than S1 which bore communicates with the atmosphere. The spring |81 having a force F tending to hold the valve on its seat together with the force ptSi-Sz) exerted upon the annular face |63.

The Valve is also subjected to the pressure which exists in the chamber I8l1 by its face S1. It lifts when this pressure reaches a value p such that pS1 is greater than p(S1-S2)-i-F. The chamber comprised between the exhaust orifices l2 and the front end of the cylinder and the chamber comprised between this same end and the front face of the piston at the moment when the plunger 22 engages in the bore 41 are calculated in a ratio such that the pressure between the piston and the front end of the cylinder exceeds p a little before this moment.

The valve I8 therefore lifts at the end of the forward stroke of the piston '2 and then remains raised through the commencement of the backward stroke until the piston 21 uncovers the orifices I2 at the back (the pressure in the chamber |84 then falls below p" and the valve falls back) A description will now be .given of the particular arrangements ofthe tool holding piston. I n front of the piston 5 engaged in the bore 42 this piston comprises a collar 51 which moves in a chamber 53 lled with oil (it communicates through the perforations 44 vwith the rear face of the member 4). This collar abuts forwardly against the end of the bore |11 and at the rear against the end of the bore 43. The diameters of these bores have been adjusted so as to be slightly greater than the diameter of the colla-r 51 so that the tool holding piston will be brakcd progressively before abutting either at the front or at the back. Shocks will thereby be avoided which may be produced either when the tool receives an impulse towards the front without encountering asuflclent resistance or when it rebounds backwards.

To the front of the collar 51 the tool holding piston comprises a cylindrical bearing sliding in the bore in the member il and passing through the stuffing box |'|2.

The arrangements employed for reducing the recoil are constructed in the following mannen- Upon the tool holding piston in front of the member Il is screw-threaded a piston 28 movable in the bore`232 of the member 23 screwed upon the body of the machine. The rear face of this piston is placed at atmospheric pressure through the orifices 233. The front face is subjected to the pressure p through the duct |55. The reaction thus produced upon the body having the effect of ,reducing the recoil.

Only the arrangements provided for automatically stopping the tool under no load have now to be described. They consist in cutting off the supply of compressed air when the tool holding piston advances a certain distance from its rear abutment. For this purpose, the chamber |8 in which the pressure pr exists can be separated from the chamber I9 into which the compressed air duct 22 leads by means of the cylindrical slide valve E8. This slide valve comprises two cylindrical seatings |81, |82 of the same diameter connected together by a central rod. The outer face of the seating |81 is subjected to atmospheric pressure.

A spring |83 bears upon this face and tends to press the slide valve against the seating |85. In this position the seating $81 covers the opening through which the chamber |D communicates with the bore of the slide valve |8 and cuts off the admission.

,The slide valve i8 opens the admission when it has effected a certain stroke towards the rear against the reaction of the spring. The outer face of the seating |82 communicates on the one hand through the small orifice |81 with the compressed. air and on the other hand through the duct |8s with a chamber 231 formed in the bore which guides the tool holder forward of the member 23.

The tool holder which slides in this bore has a circular groove 52 which is entirely covered by the part 23 when the tool holder is against its rear abutment and which is uncovered at the front and puts the chamber 231 into communi-- cation with the atmosphere when the tool holder is pressed against its front seating.

In this position the pressure against the face |82 falls :to atmospheric pressure, the orice I84 being much smaller than the leak orifice formed by the duct |86 and the space comprised between the groove 52 and the bore of the part 23.

The slide valve I8 under the action of its spring I83 comes into Contact with its abutment I85 and the admission of compressed air is cut off. On 'the contrary, when the tool holder is pressed against its rear abutment the Vleak Vorifice is closed, the pressure rises under the face I82 and the slide valve I8 opens for the vadmission of compressed air. A

This automatic stopping device operates at the Y same time as a regulating device. When the tool holder advances too quickly or when the operative does not balance the recoil of the machine at full power the tool holder automatically commences to move about the position which uncovers the groove 52 at the front. The slide valve I8 moves about the position which opens the admission and the latter is throttled so that the recoil of the machine balances the eiort applied to the body by the operative.

This leads to the provision of a compressed air relay between the two members and the arrangement described above is obtained in this way.

Naturally, means are provided upon the apparatus for permitting it to be handled and used.

What I claim is:-

1. A pneumatic tool comprising a body having fluid filled bores, a cylinder in said body having an admission orifice, a piston movable by compressed air in said cylinder, a tool holding piston movable in one of. said bores, a plunger piston rigid with the first mentioned piston and movable in another of the fluid filled bores, a discharge chamber having an outlet end, the second mentioned bore leading to the bore of the tool holding piston and traversing said discharge chamber, the outlet end of said chamber being closed by the plunger piston at the end of its travel and the fluid then interposed between said plunger and the tool holding piston being limited, a displaceable member, said body having a chamber receiving said member and communicating with said admission orice, said member constituting a slide valve for said orice, and means connecting said* discharge chamber with the second mentioned chamber whereby the fluid drawn in and delivered by the piston plunger in the discharge chamber displaces said member.

2. A pneumatic tool as claimed in claim 1 characterized by the provision of a uid containing chamber in said body, an impervious elastic diaphragm constituting a part of the wall of said fluid containing chamber, and means for subjecting the diaphragm to air pressure.

3. A pneumatic tool as claimed in claim 1 characterized by the provision of a iuid containing chamber in said body, an impervious elastic diaphragm constituting a part of the Wall of said fluid containing chamber, and means for subjecting the diaphragm to air pressure, a differential piston actuated by the fluid drawn in and delivered by the piston plunger in the discharge chamber, said differential member hav.

ing one side presented to the discharge chamber and having two faces on the opposite side thereof, the total area of the two faces being equal to the total area of the rst mentioned side of. the diiferential member, one of said faces being exposed to the fluid contained in said iiuid containing chamber and the other face being of smaller area than the rst mentioned face and adapted to move fluid toward and away from said displaceable member, and means acting when the differential piston is at the ends of its travel to open communication between the discharge chamber and the iluid containing chamber.

4. A pneumatictool as claimed in claim 1 characterized by the provision of a fluid containing chamber in said body, animp'er'vio'us elastic diaphragm constituting apart of the wall of said fluid containing chamber, vand-means for subjecting the diaphragm Yto air pressure, a differential piston 'actuated by the' fluid Ydrawn in and delivered-by the piston plunger in theA'di'scharge chamber, said differential member having one side presented to the discharge chamber and having two faces on the opposite side thereof, the total area of the two faces being equal to the total area of the first mentioned side of the differential member, one of said faces being exposed to the fluid contained in said fluid containing chamber and the other face being of smaller area than the rst mentioned face and adapted to move fluid toward and away from said displaceable member, and means acting when the differential piston is at the ends of its travel to open communication between the discharge chamber and the fluid containing chamber, a double automatic valve interposed between the dilferential piston and said displaceable member, said double valve producing a xed loss of charge upon the passage of the uid from the displaceable member to the differential piston and a higher loss of charge upon the reverse passage of fluid from the differential piston to the displaceable member, a passage in said body connecting the differential piston and the fluid containing chamber, a piston having limited movement in the last mentioned passage, a passage of reduced area for the passage of fluid between the uid containing chamber and the space between the differential piston and the displaceable member, and a valve controlled passage arranged to permit passage of uid from the fluid containing chamber to the space between the differential piston and the displaceable member but obstructing the passage of uid in the opposite direction.

5. A pneumatic tool as claimed in claim 1 characterized by the provision of air orices at the front end of said cylinder, a valve normally closing said orices, a spring normally tending to close said valve, said valve being also subjected to air pressure from the air supply to said cylinder whereby said valve is normally held in closed position.

6. A pneumatic tool as claimed in claim 1 characterized in that said tool holding piston includes a collar, a fluid lled chamber in said body receiving said collar and having walls constituting stops for the tool holding piston, said walls having grooves therein of slightly greater diameter than said collar for receiving the latter in the opposite positions of the toolholding piston.

7. A pneumatic tool Yas claimed in claim 1 characterized by the provision of a damping piston rigid with the tool holding piston, a chamber in said body receiving the damping piston having communication with the atmosphere at the rear of said actuating piston, and means for supplying compressed air to the front face of the damping piston.

8. A pneumatic tool as claimed in claim 1 characterized by the provision of a uid containing chamber in said body, an impervious elastic diaphragm constituting a part of the wall of said fluid containing chamber, and means for subjecting the diaphragmto air pressure, a rege ulating slide valve movable in said admission orifice in advance of the displaceable member with reference to the direction of flow of air,

a groove, therein, means communicating with the air admitted tothe regulating slide valve and connected with said guide whereby in one position of the tool the groove therein establishes communication between the last mentioned communicating means and the atmosphere. *e

GEORGES BRUN. 

